The present invention relates to measurement and control systems for the delivery of liquids under relatively high hydraulic pressures. In particular, the invention relates to a liquid pressure gauge having an indicator for providing a direct readout of pressure, and having an internal electrical switch which may be activated at certain predetermined pressures.
Pressure gauges for monitoring the pressures within a hydraulic delivery line are well known. Such pressure gauges are typically interposed into the liquid delivery conduit so as to be in direct contact with the pressurized liquid therein. A pressure-responsive element typically includes a transducer which translates liquid pressure into a physical movement, and the physical movement is mechanically linked to an indicator device. The pressure gauges which are known in the prior art include pressure gauges wherein a Bourdon tube has an opening which is in contact with the pressurized liquid, and also includes liquid-filled Bourdon tubes wherein the liquid is sealed into the tube by means of a movable diaphragm sealing disk mounted at the end of the Bourdon tube, wherein the end of the Bourdon tube is then placed in a liquid delivery conduit so as to be exposed to liquid pressures therein via the diaphragm.
Pressure control switches are also known, wherein an electrical switch activation lever is placed in proximity to a Bourdon tube pressure sensor, wherein pressure changes cause the Bourdon tube to deflect and move the switch actuator, thereby generating an electrical signal at the pressure level at which contact is made. U.S. Pat. No. 4,323,741, issued Apr. 6, 1982, and U.S. Pat. No. 4,397,610, issued Aug. 9, 1983, disclose two forms of pressure-control device wherein these principles are used.